This invention relates to a novel titanium-containing porous silica and to a process for the preparation thereof.
Isomorphously substituted Ti-containing porous silica materials are of great interest from both commercial and academic points of view because of their extraordinary potential as oxidation catalysts. The incorporation of titanium into a silicate framework results in the formation of isolated Ti centers capable of undergoing a facile coordination change and of forming an active peroxo-titanium complex upon contact with H.sub.2 O.sub.2 and TBHP (terbutyl hydroperoxide). This peroxo-titanium complex is responsible for unique selectivities in oxidation reactions of organic compounds.
A variety of Ti-containing microporous (with an average pore diameter of 2 nm or less) or mesoporous (with an average pore diameter of 2-50 nm) silica materials, such as TS-1, TS-2, Ti-Beta, Ti-MCM-41 and Ti-MCM-48, have been developed in recent years. Ti-containing microstructured materials are prepared by use of a molecular templating agent, whereas a liquid crystal templating agent with cooperative assembly of surfactants and inorganic species is used for the preparation of mesostructured materials. Initial attempts at incorporation of titanium into micro- or mesostructured materials have shown that up to 3 mol % titanium can be isomorphously substituted into a silicate framework. The major problem in the preparation of Ti-containing silica is domain formation due to a difference in reactivity between titanium and silicon alkoxides. Modification of the highly labile titanium alkoxide by chelation and prehydrolysis of the less reactive silicon alkoxide has been proposed for compensating for the differences in hydrolysis and condensation rates of these compounds. However, the resultant material has the properties of amorphous titanium-silicon mixed oxides.